1. Field of the Invention
The present invention relates to a focus detection apparatus for, e.g., a camera and, more particularly, to an auto-focus apparatus for performing focus detection using an auxiliary light source.
2. Related Background Art
Conventionally, in an auto-focus apparatus for performing focus detection using an image signal accumulation sensor such as, e.g., a CCD, and driving a lens based on a focus detection result, precise focus detection is disabled in a low-contrast state. For this reason, in a low-contrast state, a method of projecting auxiliary light onto an object, and performing focus detection is adopted.
However, conventionally, the low-contrast determination level is set at a boundary level allowing focus detection without auxiliary light. For this reason, focus detection can be performed without auxiliary light in a slightly higher contrast state than that at the boundary level. In such a contrast state, focus detection precision is low, and auxiliary light should be projected in such a contrast state to attain focus detection with high precision. Therefore, if the auxiliary light projection determination level is set at a determination level (4.times.LCNUM) higher than the boundary determination level (LCNUM) allowing focus detection without auxiliary light, the above-mentioned problem can be solved.
On the other hand, in an apparatus of this type, a focus detection enable/disable determination level is caused to coincide with the auxiliary light projection determination level since auxiliary light is projected when the focus detection is disabled. Therefore, when the auxiliary light projection determination level is set to be 4.times.LCNUM, as described above, the focus detection enable/disable level is also set to be 4.times.LCNUM. Therefore, when a contrast state as a result of projection of auxiliary light corresponds to a contrast between LCNUM and 4.times.LCNUM, it is determined that the focus detection is disabled although a focusing operation can be performed, and the focusing operation is inhibited.